Project Summary/Abstract This project will focus on the development and in vivo characterization of small molecule inhibitors of HOXA13 as a therapy for reducing tumor vascularization. During embryogenesis, HOX proteins direct tissue and organ development by regulating clusters of genes whose products control tissue specification and differentiation. We have established that HOXA13 regulates a cluster of pro-vascular genes necessary for vascular development in the developing embryo. More importantly, we have determined that many of the same provascular genes are regulated by HOXA13 in the developing vasculature of hepatocarcinomas. Because HOXA13 functions in a pleiotropic manner to regulate vascular development, I hypothesize that the disruption of HOXA13's transcriptional function would effectively inhibit tumor vascularization by simultaneously affecting the expression of a cohort genes required for tumor vasculogenesis. Recognizing that DNA binding is required for HOXA13's transcriptional function, we developed a small molecule screen to identify compounds capable of preventing HOXA13 from interacting with its target DNA sequence. From this screen, we identified Compound B (CpdB), a small molecule that can partially inhibit HOXA13's ability to regulate a group of provascular genes. Through careful modifications to CpdB's initial structure, I hypothesize that the efficacy of this small molecule can be improved to inhibit HOXA13 function in developing tumors. To test this hypothesis, the following specific aims will be accomplished: Aim 1. Determine the specificity of CpdB for HOXA13. Aim 2. Quantitate the affinity of CpdB for HOXA13 and determine which amino acid residues within the HOXA13 DNA binding domain are contacted by CpdB. Aim 3. Determination of structure activity relationships for HOXA13 and CpdB, optimization of CpdB potency, and improvement of CpdB solubility. Aim 4. Determine the efficacy of CpdB analogs to perturb HOXA13-regulated provascular gene expression in developing tumors.